The invention relates to mattresses in general, and more particularly to improvements in mattresses of the type wherein a base has a recess which is provided in its upper side and receives a removable insert, the base and the insert being confined in a mattress cover.
Commonly owned German Utility Model No. G 89 00 196 discloses a mattress wherein the base consists of a single piece of foamed material having a constant density. The upper side of the base is formed with an elongated recess which extends practically all the way between the foot end and the head end and serves to receive an insert of the type disclosed in commonly owned European Pat. No. 0 236 668. The insert has a covering which confines an envelope for several superimposed layers of foamed material.
Austrian Pat. No. 230048 to Liebknecht discloses a mattress wherein the base contains a first set of springs and the insert in the recess at the upper side of the base contains a second set of springs. The springs of the base beneath the recess are harder than the other springs of the base, and the recess extends substantially all the way from the foot end to the head end of the mattress. Two cushioning covers surround the base and the insert in its upper side. An impermeable partition is inserted into the recess to overlie the underside as well as the front and lateral sides of the insert.
German Utility Model No. 7007643 of de Smedt discloses a head support which can be used as a cushion and is made of a cellular elastic mass with a valley between two hills at its upper side. The valley receives the head of the person utilizing the cushion.
Commonly owned U.S. Pat. No. 4,777,681 discloses a cushion which contains a stuffing of foamed material. The patented cushion is intended for use in toys, beds, clothing, mattresses, motor vehicles and upholstered furniture. A case of the cushion contains a stuffing having one or more layers of foamed material with straight slits extending between opposite sides of the layer.
A drawback of presently known mattresses and their constituents is that they do not meet several often contradictory requirements, especially for use by patients afflicted with certain types of illnesses and infirmities. For example, a mattress should be reasonably hard but not so hard that the occupant is compelled to assume different positions at frequent intervals in order to relieve those parts of her or his body which were in contact with the upper side of the mattress. On the other hand, a satisfactory mattress should not be too soft because this would cause the body of the occupant to sink into the upper side of the mattress and to be impeded in her or his movements. Moreover, a relatively soft mattress interferes with the breathing of a substantial part of the skin of an occupant.
Furthermore, a satisfactory mattress should exhibit a highly localized elasticity, i.e., it should yield only at the very locus of application of a deforming force. The diameter of the deformed portion should be very small without a gradual and extended transition into the surrounding non-deformed areas. The construction should be such that the mattress will yield to the buttocks and to the hips of an occupant but its deformation should be much less pronounced or practically zero in the lumbar region of the person resting on the mattress.
Still further, a satisfactory mattress must satisfy certain biomechanical (i.e., orthopedic) requirements as well as certain physiological (microclimatic) desiderata.